In general, mobile communication systems were developed to provide voice services while providing activity to users. However, the fields of use for the mobile communication systems have extended to providing data services beyond providing the voice communication service, and mobile communication systems have now developed to such a level at which they can provide high speed data service. Meanwhile, to present, resource shortages have arisen in the mobile communication systems providing services, and due to users' demands for higher speed services, more developed mobile communication systems are required.
To meet the demands, standardization of Long Term Evolution (LTE) is being progressed by the 3rd Generation Partnership Project (3GPP) as one of the next generation mobile communication systems that are being developed. The LTE is a technology of implementing high speed packet based communication with a transmission rate of up to about 100 Mbps. To this end, several methods are being discussed, including a method of reducing the number of nodes located on a communication channel by simplifying network architecture, a method of making wireless protocols closely access a wireless channel to the maximum, and the like.
In such mobile communication systems, user equipment can simultaneously use a plurality of different types of networks. In particular, the user equipment can simultaneously use 3GPP access networks such as GERAN (GSM (Global System for Mobile communications) EDGE (Enhanced Data Rates for GSM Evolved) Radio Access Network)/UTRAN (UMTS (Universal Mobile Telecommunication System) Terrestrial Radio Access Network)/E-UTRAN (Evolved UMTS Terrestrial Radio Access Network) and non-3GPP access networks such as WLAN. For example, the user equipment may access WLAN for different traffic to transmit/receive data while accessing E-UTRAN to transmit/receive data.